Systems that enable any one of a number of signal sources to be routed to any one of a number of signal destinations are well known. The signals may be analog audio, analog video or digital data; in the remainder of this specification the term ‘data’ will be used to include all of these signal types. In the broadcast industry such systems are known as ‘routers’ or ‘switching matrices’ and large systems may have hundreds of sources and or destinations. The failure of a router usually has severe consequences for the operability of a broadcast facility, and it is therefore common for so-called ‘redundant’ distribution topologies to be used in which alternative data paths can be substituted for paths blocked by hardware failures.
A typical broadcast router comprises: a number of input modules that adapt incoming signals to a convenient format for switching and distribution within the router; a number of ‘crosspoint’ modules that select particular signals for onward distribution to specific destinations; and, a number of output modules that adapt the internal signal format to the format required at the output of the router. Generally all the modules comprise plug-in printed-circuit assemblies that can be removed or replaced by the user. Known methods for providing redundancy against the failure of a crosspoint include the provision of one or more additional crosspoint modules. In one such system an additional, redundant crosspoint module has its inputs paralleled with those of an existing crosspoint module and its outputs are connected to secondary inputs of the output modules fed by the existing crosspoint module. The output modules are provided with two-way switches at their inputs so that the signal from the ‘redundant’ crosspoint can be selected if the normal crosspoint module should fail.
The very high data rates associated with high-definition television require impedance-matched transmission lines to be used for the interconnection of the components of a router and this can complicate the provision of additional connections to redundant crosspoints.